High resolution fine patterning is an important process for device fabrication. FIG. 1 illustrates the conventional method for producing an isolated image on a photoresist which involves using a chrome on glass mask (COG) 50 with a chrome dot 22. A single exposure is performed through COG mask 50 to transfer a dot image to the substrate. For a positive photoresist on a wafer, the chrome dot will block a region from being exposed. After development, a dot 75 is formed at the unexposed region of the wafer 100 as shown in FIG. 1.
Future generations of microelectronic devices necessitate smaller critical dimensions. The dots produced by the method of FIG. 1 gradually become deformed as they are scaled to smaller sizes. FIGS. 2A-2D illustrate images obtained using the conventional process of FIG. 1. FIG. 2A depicts a relatively smooth dot of 250 nm diameter. Similarly, a smooth dot having a size of 200 nm (FIG. 2B), and as low as 160 nm (FIG. 2C) can also be formed using the prior method. At just below 150 nm, dots produced by the process of FIG. 1 begin to show distortion as indicated by FIG. 2D. Thus, FIGS. 2A-2D demonstrate that the images developed with the prior method become deformed as the resolution is decreased below 150 nm. Therefore, a new method is needed for achieving an isolated image on a photoresist for microelectronic fabrication.